期刊
JOURNAL OF INFECTIOUS DISEASES
卷 207, 期 5, 页码 794-802出版社
OXFORD UNIV PRESS INC
DOI: 10.1093/infdis/jis755
关键词
Salmonella; ramA; ramR; cell invasion; multidrug resistance; efflux; fluoroquinolone; type III secretion-system 1; transcriptional regulation
资金
- Institut National pour la Recherche Agronomique (INRA) as an INRA-JSPS (Japan Society for the Promotion of Science)
- French Region Centre [2008 00036085]
- European Union [1634-32245]
Background. Fluoroquinolone (FQ) resistance is increasing worldwide among Salmonella species. Among the mechanisms involved, increased efflux via the tripartite AcrAB-TolC efflux system is mainly modulated through control of expression via the ramRA regulatory locus gene products. Interestingly, in some reference strains these have also been experimentally shown to regulate cell invasion-related genes of the type III secretion system 1 (T3SS-1). In this study, we investigated whether natural mutations occurring in this locus in FQ-resistant S. enterica serovar Typhimurium epidemic clones resulted in the same effects. Methods. Quantitative reverse transcription polymerase chain reaction and cell invasion assays were used to study 3 clinical FQ-resistant S. Typhimurium isolates representative of the DT104 and DT204 epidemic clones. For comparison, 3 control reference quinolone-susceptible strains were included. Results. As previously shown, the investigated mutations altering RamR or its DNA-binding site increased expression of efflux genes dependently on ramA. However, the decreased expression of T3SS-1 genes previously reported was not always observed and seemed to be dependent on the genetic background of the FQ-resistant isolate. Indeed, a ramA-dependent decreased invasion of intestinal epithelial cells was only observed for a particular clinical ramR mutant. Conclusions. ramRA mutations occurring in clinical FQ-resistant S. Typhimurium isolates may negatively modulate their invasiveness but this is strain-dependent.
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